Block Pulled Up Slope/Coefficient Of Kinetic Friction.

[kaylanp01]

Homework Statement

Block A has a mass of 5.56 kg and is on a rough incline of 21.5 degrees to the horizontal. Block B has a mass of 4.66 kg and the coefficient of kinetic friction between Block A and the plane is 0.276. What is the acceleration of the blocks?

Homework Equations

I used a = m2g - m1gsin(theta) / (m1+m2)
I see why that's wrong though, because I didn't use the kinetic friction.

The Attempt at a Solution

Again, I used the eq above to get
a = (4.66)(9.81) - (5.56)(9.81)sin(21.5) / (5.56+4.66) = 2.52 m/s^2

But I see why that's incorrect, I just don't know the correct method. haha.

Thanks! :)

 

[Doc Al]

I don't understand the setup. How are the two blocks related?

 

[kaylanp01]

I don't understand the setup. How are the two blocks related?

just a sec, i'll draw a picture.

Sorry that it took me a while to reply, I'm still working on the remaining questions.

 

[Doc Al]

I used a = m2g - m1gsin(theta) / (m1+m2)
I see why that's wrong though, because I didn't use the kinetic friction.

Well then, add the kinetic friction. What's the formula for finding the friction force? What's the normal force?

 

[kaylanp01]

Well then, add the kinetic friction. What's the formula for finding the friction force? What's the normal force?

I have N=f/mu but I don't know F or N. Hah. I'm usually not this terrible at physics, I promise.

 

[Doc Al]

To find the normal force, analyze forces on the block perpendicular to the incline surface.

 

[kaylanp01]

To find the normal force, analyze forces on the block perpendicular to the incline surface.

See, that's the part that confuses me, the drawing of the arrows on the diagram. How do you know what direction N is pointing in? Whats mg? Etc.

I'm really not understanding this entire topic.